Add ppool_supersup module
Add ppool_sup module
Add ppool_worker_sup module
Add ppool_serv module
Add child spec for worker_sup to ppool_serv
Add state record to ppool_serv
Add ppool_serv init/1 and handle_info/2 functions
Add ppool_serv:handle_call/3
Add ppool_serv:handle_cast/2
Add ppool_serv:handle_info/2 function head for down workers
Add ppool_serv:code_change/3
Add ppool_serv:terminate/2
Add ppool API module to interface with the ppool_supersup and ppool_serv
Add ppool_nagger module to demo the use of ppool application